1. Field of the Invention
The present invention relates to an exchange coupling film for fixing a magnetization direction of a ferromagnetic body, a magnetoresistance effect device incorporating the same which causes a substantial magnetoresistance change with a low magnetic field, a magnetoresistance head incorporating the same which is suitable for use in high density magnetic recording and reproduction, and a method for producing such an exchange coupling film.
2. Description of the Related Art
In recent years, the density of hard disk drives has been dramatically increased, while reproduction magnetic heads have also been improved dramatically. Among others, a magnetoresistance effect device (hereinafter, referred to simply as an xe2x80x9cMR devicexe2x80x9d) utilizing a giant magnetoresistance effect, which is also called a xe2x80x9cspin valvexe2x80x9d, has been researched actively and is expected to have the potential to significantly improve the sensitivity of a currently-employed magnetoresistance effect head (hereinafter, referred to simply as an xe2x80x9cMR headxe2x80x9d).
A spin valve includes two ferromagnetic layers and a non-magnetic layer interposed between the ferromagnetic layers. The magnetization direction of one of the ferromagnetic layers (hereinafter, referred to also as a xe2x80x9cpinned layerxe2x80x9d) is fixed by an exchange bias magnetic field from a pinning layer (the ferromagnetic layer and the pinning layer are referred to collectively as an xe2x80x9cexchange coupling filmxe2x80x9d). The magnetization direction of the other one of the ferromagnetic layers (hereinafter, referred to also as a xe2x80x9cfree layerxe2x80x9d) is allowed to change relatively freely in response to an external magnetic field. In this way, the angle between the magnetization direction of the pinned layer and that of the free layer is allowed to change so as to vary the electric resistance of the MR device.
A spin valve film has been proposed which utilizes Nixe2x80x94Fe for the ferromagnetic layer, Cu for the non-magnetic layer and Fexe2x80x94Mn for the pinning layer. The spin valve film provides a magnetoresistance rate of change (hereinafter, referred to simply as an xe2x80x9cMR ratioxe2x80x9d) of about 2% (Journal of Magnetism and Magnetic Materials 93, p. 101, (1991)). When Fexe2x80x94Mn is used for the pinning layer, the resulting MR ratio is small, and the blocking temperature (a temperature at which the pinning layer provides no effect of fixing the magnetization direction of the pinned layer) is not sufficiently high. Moreover, the Fexe2x80x94Mn film itself has a poor corrosion resistance. In view of this, other spin valve films have been proposed which employ pinning layers with materials other than Fexe2x80x94Mn.
Among others, a spin valve film which employs an oxide, such as NiO or xcex1-Fe2O3, for the pinning layer is expected to realize a dramatically large MR ratio of about 15% or greater.
However, the blocking temperature of NiO is not sufficiently high. Therefore, the thermal stability of the MR device employing NiO is undesirable.
When a spin valve film employs a pinning layer of xcex1-Fe2O3, on the other hand, the reverse magnetic field of the pinned layer is not sufficiently large when the pinning layer is thin. Particularly, a spin valve film having a dual spin valve structure or a spin valve film where an xcex1-Fe2O3 layer is formed on the pinned layer has a strong tendency that the reverse magnetic field of the pinned layer obtained in the overlying xcex1-Fe2O3 layer is insufficient. Moreover, the thermal stability of the xcex1-Fe2O3-employing spin valve film is also undesirable for the same reasons as the NiO-employing spin valve film. Furthermore, the xcex1-Fe2O3-employing spin valve film has other problems in controlling the anisotropy during deposition in a magnetic field or during a low-temperature heat treatment in a magnetic field.
According to one aspect of this invention, an exchange coupling film includes a ferromagnetic layer and a pinning layer which is provided in contact with the ferromagnetic layer for pinning a magnetization direction of the ferromagnetic layer, the pinning layer including an (AB)2Ox layer, wherein: O denotes an oxygen atom; 2.8 less than x less than 3.2; and a value t as defined by:
t=(Ra+Ro)/(2xc2x7(Rb+Ro)) 
(where Ra, Rb and Ro denote the ion radii of the atoms A, B and O, respectively)
satisfies 0.8 less than t less than 0.97.
In one embodiment of the invention, the (AB)2Ox includes an antiferromagnetic layer.
In another embodiment of the invention, the atom B of the (AB)2Ox layer includes a transition metal atom.
In still another embodiment of the invention, the atom B of the (AB)2Ox layer includes an Fe atom.
In still another embodiment of the invention, the atom A of the (AB)2Ox layer includes a rare earth atom.
In still another embodiment of the invention, the atom A of the (AB)2Ox layer includes an alkaline-earth atom.
In still another embodiment of the invention, the pinning layer includes a layered structure of the (AB)2Ox layer and an NiO layer.
In still another embodiment of the invention, the (AB)2Ox layer is provided in contact with the ferromagnetic layer.
In still another embodiment of the invention, the pinning layer includes a layered structure of the (AB)2Ox layer and an Fexe2x80x94Mxe2x80x94O layer (where M=Al, Ti, Co, Mn, Cr, Ni or V).
In still another embodiment of the invention, the Fexe2x80x94Mxe2x80x94O layer includes an (Fe1-xMx)2O3 layer (where M=Al, Ti, Co, Mn, Cr, Ni or V, and 0.01xe2x89xa6xxe2x89xa60.4).
According to another aspect of this invention, a magnetoresistance effect device includes a substrate and a multilayer film. The multilayer film includes at least two ferromagnetic layers, a non-magnetic layer and a pinning layer for pinning a magnetization direction of the ferromagnetic layer. The ferromagnetic layers are deposited via the non-magnetic layer interposed therebetween. At least one of the ferromagnetic layers is a pinned layer whose magnetization direction is fixed by the pinning layer which is provided in contact with the one of the ferromagnetic layers on an opposite side of another one of the ferromagnetic layers with respect to the non-magnetic layer. At least one of the ferromagnetic layers is a free layer whose magnetization direction is allowed to rotate freely. A change in an angle between the magnetization direction of the pinned layer and the magnetization direction of the free layer causes an electric resistance of the device to vary. The pinning layer includes an (AB)2Ox layer, wherein: O denotes an oxygen atom, 2.8 less than x less than 3.2; and a value t as defined by:
t=(Ra+Ro)/(2xc2x7(Rb+Ro)) 
(where Ra, Rb and Ro denote the ion radii of the atoms A, B and O, respectively)
satisfies 0.8 less than t less than 0.97.
In still another embodiment of the invention, the pinning layer includes a layered structure of the (AB)2Ox layer and an NiO layer.
In still another embodiment of the invention, the pinning layer includes a layered structure of the (AB)2Ox layer and an Fexe2x80x94Mxe2x80x94O layer (where M=Al, Ti, Co, Mn, Cr, Ni or V).
In still another embodiment of the invention, the atom B of the (AB)2Ox layer includes a transition metal atom.
In still another embodiment of the invention, the atom A of the (AB)2Ox layer includes a rare earth atom.
In still another embodiment of the invention, the atom A of the (AB)2Ox layer includes an alkaline-earth atom.
In still another embodiment of the invention, AB of the (AB)2Ox layer includes La1-yFey(0.4 less than y less than 0.6).
In still another embodiment of the invention, the atom A of the (AB)2Ox layer includes an Axe2x80x2 atom or an Axe2x80x3 atom, and the atom B of the (AB)2Ox layer includes an Bxe2x80x2 atom or an Bxe2x80x3 atom. The Axe2x80x2 atom includes a rare earth atom; the Axe2x80x3 atom includes an alkaline-earth atom; the Bxe2x80x2 atom includes an Fe atom; and the Bxe2x80x3 atom includes an Ni or Mn atom.
In still another embodiment of the invention, the Axe2x80x2 atom includes an La atom; the Axe2x80x3 atom includes an Sr atom; the Bxe2x80x2 atom includes an Fe atom; and the Bxe2x80x3 atom includes an Ni atom.
In still another embodiment of the invention, the free layer includes two or more magnetic films deposited via the non-magnetic layer interposed therebetween.
In still another embodiment of the invention, the pinned layer includes two magnetic layers having an antiferromagnetic exchange coupling therebetween via the non-magnetic layer interposed therebetween.
In still another embodiment of the invention, the multilayer includes a first pinning layer, a first pinned layer, a first nonmagnetic layer, a ferromagnetic free layer, a second non-magnetic layer, a second pinned layer and a second pinning layer which are deposited in this order on the substrate. The first pinning layer fixes a magnetization direction of the first pinned layer. The second pinning layer fixes a magnetization direction of the second pinned layer. The first pinning layer includes the (AB)2Ox layer.
In still another embodiment of the invention, the second pinning layer includes a T-Mn (where T=Ir, Pt, Pd, Rh, or Ni).
In still another embodiment of the invention, the second pinning layer includes the (AB)2Ox layer.
In still another embodiment of the invention, the first pinning layer or the first and second pinning layers include a layered structure of the (AB)2Ox layer and an NiO layer.
In still another embodiment of the invention, the first pinning layer or the first and second pinning layers include a layered structure of the (AB)2Ox layer and an Fexe2x80x94Mxe2x80x94O layer (where M=Al, Ti, Co, Mn, Cr, Ni or V).
In still another embodiment of the invention, the Fexe2x80x94Mxe2x80x94O layer includes an (Fe1-xMx)2O3 layer (where M=Al, Ti, Co, Mn, Cr, Ni or V, and 0.01xe2x89xa6xxe2x89xa60.4).
In still another embodiment of the invention, the atom B of the (AB)2Ox layer includes an Fe atom.
In still another embodiment of the invention, the atom A of the (AB)2Ox layer includes a rare earth atom.
In still another embodiment of the invention, the atom A of the (AB)2Ox layer includes an alkaline-earth atom.
In still another embodiment of the invention, AB of the (AB)2Ox layer includes La1-yFey (0.4 less than y less than 0.6).
In still another embodiment of the invention, the atom A of the (AB)2Ox layer includes an Axe2x80x2 atom or an Axe2x80x3 atom, and the atom B of the (AB)2Ox layer includes an Bxe2x80x2 atom or an Bxe2x80x3 atom. The Axe2x80x2 atom includes a rare earth atom; the Axe2x80x3 atom includes an alkaline-earth atom; the Bxe2x80x2 atom includes an Fe atom; and the Bxe2x80x3 atom includes an Ni or Mn atom.
In still another embodiment of the invention, the Axe2x80x2 atom includes an La atom; the Axe2x80x3 atom includes an Sr atom; the Bxe2x80x2 atom includes an Fe atom; and the Bxe2x80x3 atom includes an Ni atom.
In still another embodiment of the invention, the free layer includes two or more magnetic films deposited via the non-magnetic layer interposed therebetween.
In still another embodiment of the invention, the pinned layer includes two magnetic layers having an antiferromagnetic exchange coupling therebetween via the non-magnetic layer interposed therebetween.
According to still another aspect of this invention, a magnetoresistance effect head includes: a magnetoresistance effect device of the present invention; and a shield gap section for insulating the magnetoresistance effect device and the shield section from each other.
According to still another aspect of this invention, a magnetoresistance effect head includes: a magnetoresistance effect device of the present invention; and a yoke section for introducing into the magnetoresistance effect device a magnetic field to be detected.
According to still another aspect of this invention, a method for producing an exchange coupling film includes the steps of: heating a substrate to a temperature of about 300xc2x0 C. or higher; and depositing the exchange coupling film by a sputtering method using an Ar gas at a pressure of about 2 mTorr or less.
In order to solve the problems in the prior art, the exchange coupling film of the present invention is formed by depositing a ferromagnetic layer and an (AB)2Ox layer for fixing the magnetization direction of the ferromagnetic layer. Herein, O denotes an oxygen atom; 2.8 less than x less than 3.2; and a value t as defined by:
t=(Ra+Ro)/(2xc2x7(Rb+Ro)) 
(where Ra, Rb and Ro denote the ion radii of the atoms A, B and O, respectively)
satisfies 0.8 less than t less than 0.97.
The expression (AB)2Ox indicates that the composition ratio of the total of the A and B elements with respect to the O element is 2:X (i.e., (A1-yBy)2Ox). While both of the A element and the B element should be included, the ratio between the A element and the B element may be arbitrary (preferably, such that 0.4 less than y less than 0.6). Particularly, when the A element and the B element are included at a ratio of 1:1, the resultant composition will be A1B1Ox, which will hereinafter represented as xe2x80x9cABOxxe2x80x9d. A representative example of ABO3, among others, is one which has a crystalline structure called a xe2x80x9cperovskite structurexe2x80x9d.
When the exchange coupling film is deposited on a substrate, which has been heated to a temperature of about 300xc2x0 C. or higher, by sputtering using an Ar gas at a pressure of about 2 mTorr or less, the exchange coupling film exhibits a greater exchange coupling and preferable characteristics for use as an MR device. During the deposition step, it is preferable to apply a magnetic field in the film plane so as to fix the axis of easy magnetization.
While the above-described (AB)2Ox layer is basically used as a film to be coupled with the ferromagnetic layer, desirable structures thereof include the following:
(1) An (AB)2Ox layer in which B is Fe;
(2) An (AB)2Ox layer in which A is a rare earth atom;
(3) An (AB)2Ox layer in which A is an alkaline-earth atom;
(4) A layered structure of an (AB)2Ox layer and an NiO layer;
(5) A layered structure of an (AB)2Ox layer and an Fexe2x80x94Mxe2x80x94O layer (where M=Al, Ti, Co, Mn, Cr, Ni or V); and
(6) A structure of (5), in which the Fexe2x80x94Mxe2x80x94O layer is an (Fe1-xMx)xe2x80x94O layer (where M=Al, Ti, Co, Mn, Cr, Ni or V, and 0.01xe2x89xa6xxe2x89xa60.4).
In the MR device of the present invention, the magnetization direction of at least one of the ferromagnetic layers, which are deposited together via a non-magnetic layer interposed therebetween, is fixed by the pinning layer which is provided in contact with the one of the ferromagnetic layers on an opposite side of another one of the ferromagnetic layers with respect to the non-magnetic layer (this ferromagnetic layer is called a pinned layer). On the other hand, the magnetization direction of at least one of the ferromagnetic layers is allowed to rotate freely (this ferromagnetic layer is called a free layer). A change in the angle between the magnetization direction of the pinned layer and that of the free layer causes an electric resistance of the device to vary. The pinning layer for fixing the magnetization direction of the pinned layer may be formed of the above-described (AB)2Ox material. While the above-described (AB)2Ox layer is basically used for the pinning layer, desirable structures include the above-described structures (1)-(6).
A particularly preferable example of the (AB)2Ox layer may be an La1-yFeyOx layer (where 0.4 less than y less than 0.6, and 2.8 less than x less than 3.2) in which A is La and B is Fe.
Moreover, the (AB)2Ox layer may be such that A is Axe2x80x2Axe2x80x3, and B is Bxe2x80x2Bxe2x80x3, wherein Axe2x80x2 is a rare earth element such as Y or La, Axe2x80x3 is an alkaline-earth element such as Ca, Sr or Ba, Bxe2x80x2 is Fe, and Bxe2x80x3 is Ni or Mn, for example. In the case of a composition (Axe2x80x2Axe2x80x3)1-y(Bxe2x80x2Bxe2x80x3)yOx, y is preferably such that 0.4 less than y less than 0.6.
A particularly preferable example may be one in which Axe2x80x2 is La, Axe2x80x3 is Sr, Bxe2x80x2 is Fe, and Bxe2x80x3 is Ni.
An exemplary structure of the MR device of the present invention includes an (AB)2Ox layer as a first pinning layer, a first pinned layer of a ferromagnetic material, a first non-magnetic layer, a free layer of a ferromagnetic material, a second non-magnetic layer, a second pinned layer of a ferromagnetic material and a second pinning layer which are deposited in this order on a substrate. While the above-described (AB)2Ox layer is basically used for the first pinning layer, desirable structures include the above-described structures (1)-(6). For the second pinning layer, the (AB)2Ox layer or any of above-described structures (1)-(6) may be used. Alternatively, a T-Mn metal antiferromagnetic film (where T=Ir, Pt, Pd, Rh, or Ni) may be used.
Furthermore, the present invention includes the following two types of MR heads: an MR head which is obtained by providing a shield section to the MR device of the present invention; and an MR head which is provided with a yoke of a softmagnetic material for introducing into the MR device a magnetic field to be detected.
Thus, the invention described herein makes possible the advantages of: (1) providing an exchange coupling film having a good thermal stability and a large MR ratio; (2) providing an MR device incorporating such an exchange coupling film; (3) providing an MR head incorporating such an MR device; and (4) providing a method for producing such an MR device.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.